Conventionally, various types of rotatable connector devices for electrically connecting a fixed side and a rotatable side rotatable with respect to the fixed side to each other are known. For example, one type of rotatable connector device electrically connects elements on the side of a vehicle body of an automobile and elements on the side of a steering wheel to each other.
In general, a steering wheel of an automobile includes an airbag or the like which is required to operate without fail in emergency. Therefore, a slidable electrode or the like having low dependability of connection is not used, and a rotatable connector device having built-in flat cables or the like for connecting elements on the side of the vehicle body and elements on the side of the steering wheel to each other is used.
The above-described rotatable connector device mounted on an automobile includes a cylindrical fixed case fixed to the vehicle body and a cylindrical rotatable case attached to the steering wheel. The fixed case and the rotatable case are engaged to each other so as to be rotatable with respect to each other. In a ring-shaped accommodation space defined by the fixed case and the rotatable case, flat cables are accommodated as being wound a plurality of times.
The flat cables are connected to fixed case-side connectors provided on the fixed case, and rotatable case-side connectors provided on the rotatable case. In the ring-shaped internal accommodation space, the flat cables are wound in one direction, then is turned around in a U shape to have the winding direction thereof reversed, and is wound in the opposite direction. Owing to such a structure, the rotatable connector device can rotate the rotatable case clockwise and counterclockwise in correspondence with the number of winds of the flat cables.
The fixed case of the above-described rotatable connector device is formed of a plastic material, and as shown in FIG. 1 of Patent Document 1, is easy to mold. Therefore, the fixed case includes two members, namely, a ring-shaped flat fixed-side ring plate and an outer cylinder having a cylindrical shape and extending perpendicularly from an outer circumferential edge of the fixed-side ring plate. The fixed-side ring plate and the outer cylinder are fit to each other.
The fixed-side ring plate and the outer cylinder are coupled to each other as follows, for example. A plurality of engaging hole sections projecting from the outer circumferential edge of the fixed-side ring plate perpendicularly to the fixed-side ring plate and each having an engaging hole, and a plurality of engaging convexed sections located on an outer circumferential edge of the outer cylinder at positions corresponding to the engaging hole sections and projecting radially outward, are engaged with each other. Thus, the fixed case is formed.
In this case, since the engaging hole sections located at the plurality of positions along the outer circumferential edge, and the engaging convexed sections located at the plurality of positions along the outer circumferential edge, are engaged with each other, the fixed-side ring plate and the outer cylinder are fixed to each other strongly in a direction of a rotation axis. However, in order to facilitate a work of coupling the fixed-side ring plate and the outer cylinder, play is provided in the circumferential direction at engaging positions of the engaging hole sections and the engaging convexed sections.
Because of this, in the state where the fixed case of the rotatable connector device is assembled to the vehicle body, the outer cylinder becomes rickety easily in the circumferential direction with respect to the fixed-side ring plate, which is fixed strongly to the vehicle body by a crush rib and a snap-fit. Thus, squeaky noise is likely to be generated. Especially in the case where the rotatable connector device is attached to the vehicle body in an eccentric state, the outer cylinder becomes rickety easily in the circumferential direction, which causes a problem that the squeaky noise is likely to be generated.